Osteoporosis is a skeletal disorder characterized by reduced bone strength. It can result in increased risk to fractures, height loss, hunched backs, and pain. Bone strength is a function of bone mineral density (BMD) and bone quality. It is believed that bone mineral density peaks about the age of 30 for both men and women, and then declines gradually. Some statistics have indicated that Osteoporosis affects approximately 20 million people and is a cause of about 1.3 million fracture incidents in the United States each year. As such, screening for bone mineral density is often desired.
Several common techniques have been used to measure bone mineral density, including but not limited to bone puncture, radiation Absorptiometry of single energy x-ray systems, DEXA (dual energy x-ray Absorptiometry), and sonography.
Bone puncture can be an accurate but invasive procedure, which involves the extraction of bone mass from spine area. Such a procedure carries risk.
With regard to single energy x-ray systems, mineral loss in a person's bones can be estimated from a single energy x-ray image of a body part. In diagnosing and treating bone diseases, it is common to take radiographic images of the patient (e.g., skeletal features of the patient), then either read the images directly or perform software analysis on the images to extract information of interest. For example, in diagnosing or monitoring the treatment of Osteoporosis, one might take x-ray images of selected skeletal bones, then perform computer analysis on certain image features to determine bone volume, bone length, bone geometric changes, bone strength conditions, bone age, bone cortical thickness, and bone mineral mass.
Typically, when reading and interpreting radiographic images directly, the treating physician will refer the patient to a radiologist, who can supervise both taking the radiographic image and interpreting the image to extract desired bone information, such as bone mass and bone contour irregularities. Alternatively, if the bone analysis is done, at least partially, by a computer analysis system, the x-ray images prepared by the radiologist may be sent back to the treating physician's computer site or to another computer site for computer analysis.
DEXA is a device used by hospitals to measure bone mineral density (BMD). In DEXA, two low-dosage x-ray beams with differing energy levels are directed at a patient's spine, hip, or whole body using conventional x-ray machines. A computer calculates the content of bone mineral density based on the relationship that different bones absorb different energy levels. While some consider DEXA to be accurate, the apparatus is bulky and expensive. U.S. Pat. No. 6,816,564 (Charles, Jr.) is directed to a technique for deriving tissue structure from multiple projection dual-energy x-ray Absorptiometry.
Sonography devices measure the bone mineral density of peripheral bones, such as a heel, shin bone, or kneecap. It is recognized that the bone mineral density in the spine or hip change faster than that in heel, shin bone, or kneecap. Thus, sonography is considered by some to be not as accurate or sensitive as DEXA in the determination of bone mineral density. DEXA allows early detection of abnormal change in bone mass for its targets spine, hip, or whole body. However, sonography offers advantages of lower cost and radiation-free.
U.S. Pat. No. 6,246,745 (Bi) describes a software system for determining bone mineral density from radiographic images of a patient hand obtained from conventional x-ray imaging system.
U.S. Patent Application No. 2005/0059875 (Chung) describes a biosensor and method for bone mineral density measurement.
U.S. Patent Application No. 2005/0031181 (Bi) is directed to a system and method for analyzing bone conditions using DICOM compliant bone radiographic images.
U.S. Pat. No. 5,712,892 (Weil), commonly assigned, is directed to an apparatus for measuring the bone mineral content of an extremity.
While such systems may have achieved certain degrees of success in their particular applications, there is a need for a system and method for bone mineral density screening, particularly wherein a medical professional can readily and locally (e.g., at an office location) generate a bone mineral density report. A suitable system would be easy to use, reduced in cost, yet provide sufficient accuracy. Preferred would be an on-site screening that can be utilized by physicians, radiologists, or other medical professionals.
U.S. Provisional Patent Application No. 60/755,233 (Huo), titled BONE MINERAL DENSITY ASSESSMENT USING MAMMOGRAPHY SYSTEM, filed on Dec. 30, 2005, commonly assigned, and incorporated herein by reference, describes an imaging system and method to acquire hand x-ray images suitable for bone mineral density (BMD) screening and analysis using a mammography x-ray imaging system.
Because of the challenges to acquire hand images with adequate quality using a mammography system, there exists a need to establish a calibration procedure to perform quality assurance of the x-ray system before acquiring patient images.